SonicLink is a fully decentralized, proximal communication framework for personal devices to seamlessly discover, connect, and interact with arbitrary public installations (such as digital billboards). It establishes connections based on audio proximity when you are not on the same network: being near in physical space does not mean you are near in "network space." SonicLink uses near-ultrasonic acoustic signals that permit devices and installations to discover each other. It also exploits peer-to-peer proximal wireless networking techniques for establishing a high-bandwidth, low-latency link between the device and the installation. Possible uses include �borrowing� a large-screen TV and a camera in the public space for personal video conferencing, presenting personal notifications to a public display, and taking over neon lights for visualizing music on a phone.